Production of metal tubes in inclined rolling mills



Aprl 23, 1940. F. KocKs Er AL Z,l98,540

PRODUCTION OF METAL 'UBES IN INCLIND ROLLING MILLS Filed Jan. 12, 1938 fly] 2 z i J I 'a 'EE 1.

I Y zb P Patented Apr. 23, 1940 UNITED .STATES PAWTENT OFFICE PRODUCTION OF METAL TUBES IN INCLINED BOLLING -MILLS Fritz Kocks and Josef Mehren, Dusseldorf, Germany, assig'o's to-tle firm' Deutsche Boh'enwerke Aktiengesellschaft, Dusseldorf, Germany, a company of Germany Application 'January 12, 1938, 'Serial No. 184588 In Germany December 19, 1 936 2 Claims. (CI. -13) In one of the groups of inclined rolling mills,

the principal object is to make the pass as nea'rly as possible closed in order thereby to induce the metal being rolled to flow axially. The closure of the pass was Secured in different ways, 'for instance a large number of -thin long rolls are employed forming the so-'called pin rolling mill.

subsequently the number of rolls was reduced` and fixed guides provided between them. An-

other solution proposed was to provide two guide 2@ discs rotating at a high speed, between two -working rolls (Diescher rolling mill). These methods have in some measure solved the problem of producing finished tubes with thin walls, but

the rolling mills used for the purpose have de- %i fects partly structural andpartly practical working defects, which hinder the application of these rolling'mills.

The second group of inclined rolling mills involve the method of elongating hollow metal 30 bodies with thick walls by rolling grooves into the metal and gradually widening them. This method (Roeckner rolling mili) makes use of in- `ner and outer rolls which are both provided with bosses or shoulders, for producing' grooves in the metal, which are then gradually widen'ed.

A similar problem is presented by another method in which by suitably shaping the rolls the changing of shape of the tube is divided into a series of steps, through which the metal being 40 rolled successively passes on its rotation. The

method referred to provides for a different shape of all the rolls, which are applied uniformly over the periphery of the metal being rolled in such a manner .that the hollow body is further oper- 46 ated upon by each succeeding roll at the portion that has already been operated upon by the preceding roll. In a. modification of this method a series of pass steps are provided on each working boss or shoulder on the rolls, the steps being t 50 sucoessively traversed on the rotation' of the metal being rolled'. -Th's last mentioned method has the disadvantage thatby a number of passes the effective working surface of the rolls, (that is to say the working shoulder or T:: the "hall" of the roll, becomes rather long,

1 whereby the flow of the metal axially -is rendered' more difllcult and the i metal being rolled inclines to form a wall that in one part is thick.

If rolls are usedtthat are all difierently shaped, a a preure from one side is thereby exerted on the metal being rolled and on the mandrel that is loosely located theren, and this lateral pres-- sure likewise leads to irregular changing of shape of the tub. l w

The present inventior difiers fundamentally from existing methoda i According to the invention the necessarily closed guide for the metal being rolled may be dispensed with although, as will be understood, it is advisable to have as' many working rolls as possible pressing upon the periphery of the work. Furthermore according to the method of thepresent invention, all the rolls of therolling mil] can be shaped exactly alike and the effective working surface that causes the metal to be E@ elongated made as short as possible.

A further important improvement is that guides disposed between the 'rolls and participating in the shaping operation may be dispensed with.

Other and further features of the invention 23 will be more apparent to those skilled in the art upon a consideration of the accompanying drawing and the following description wherein several exemplary embodiments of the invention ar disclosed, 8@

In the drawing:

Fig. 1 is an elevational view of one type of roll showing the application to a hollow metal body which is illustrated in section.

Fig. 2 is a View similar to Fig. 1 illustrating a s modified form of roll.

' Figs. 3, 4, 5 and 6 are sectional views of rolls illustrating various forms of constricting pass portions.

The hollow metal body mounted on the manw drel is first reduced in diameter by a suitably shaped part of the roll until its inner surface comes into contact with the mandrel. At the portion of 'the roll gan where the inner surface of the hollow body touches the mandrel, a sharp constriction of the gap takes place between the roll section and the? mandreL'whereby thehollow metal body is elongated. This constriction of the gap remains unltorm in all'the rolls-over a definite length of the gap in order to produce the elongation in full measure and to smooth the wall of thetube. Thereupon the 'gap may be gradually opened or enlarged at the smooth part in order to round the holowmetal body. The sudden constriction of' the gan may be'of any This section has for its purpose to hold the metal suitable form', for instance the gap may be constricted with sharp edges in a single plane, or the constriction may be effected with a portion of the rolls which are rounding ofi' or conically shaped.

The tamount of'the constriction is dependent upon the reduction in the thickness of wall that is to be imparted to the hollow netal body. If the hollow metal body having a wall thicknessof five millimeters is to be rolled to provide a tube with a wall thickness, the constriction of the gap may amount advantageously to from 2.5 to 3 mm., that is to say about the whole or nearly the whole reduction in thickness of wall is obtained at this [striction takes part in the elongation, while the portion of the gap. By the helical forward movement of the' metal being rolled, the frst section of the parallel part of the gap following the concontinuation of this? parallel part serves exclusively for smoothng the wall.

From the foregoing it will be understood that the shaping of the metal can be divided into three important parts which are shown in Figure 1 wherein the hollow metal body I is rolled by the rolls@ over the eylindrical mandrel 3, to produce a tube with thin walls. In the Section 'I of the r roll or pass the hollow body l is first reduced in diameter and is brought intp contact with the mandrel rod. In the Section 'II of the roll which' being rolled as firmly as possible at the portion where it enters the rolls. This firm grip results from considerable frictional'forces being exerted on the metal being rolled by surfaces which are of corresponding length, the frictional forces drawing the metal into the rolling mill. If the metal enters the'constriction of the pass after it has passed through this additional part 'of the rolls, it becomes possible to elongate the metal being rolled at a speed that very considerably exceeds the theoretical feeding speed of the rolls. For example it is possible with a rolling mill according to the invention to allow the rolled metal to leave the rolling mill at a speed that is 65% .higher than that corresponding to the theoretical feeding speed of the rolls. This phenomenon corresponds to the method used on extrusion 'presses, wherein a hollow body with thick walls is forced with great pressure through a constriction of the pass.

The important technical improvements of the invention resides in the fact that tubes with an unusually uniform thickness of wall can be produced, having very thin walls. Hollow bodies of highly alloyed steels can be transformed into tubes with thin walls. In carrying the invention into practice tubes with walls 1 /2 mm. thick and an external diameter of 65 mm. have been produced from non-rusting steels containing 18% chromium and 8% nickel and from metals highly resistant to heat and containing 24% chromium.

The shortness of the actual working surface of the rolls provides a further improvement in that the metal being rolled is exposed to exceptionally small distortion stresses, since the distortion in inclined rolling mills is dependent upon the length or extent of engagement by the rolls.

For carrying out the invention it is of no consequence whether the rolls employed are cylin--` drical, conical or disc-shaped. The condition of importance is the pass gap which is formed by the roll section and the'mandrel. Accordingly the guiding-in and the reducing parts of the pass are according to the invention of such a shape that the metal being rolled is first drawn-in conically, the cone formed bythe working surfaces of the roll having an angle at the apex of at most about (Figure 1).

The part 'of the pass that would be adjacent the reducing cone-which may be called the pressure cone, because by it the metal being rolled is in some measure pressed through the pass constricton-has to have an angle at the apex of at most about 20 as shown in Fig. 2.

The sharp constriction of the pass may assume any form desired in the manner indicated, as shown in Figures 3 to 6. The condition for the maintenance of the fundamentals of the invention is however that the constriction is at most equal to the reduction in thickness of the wall that is to be efiected, and that the length of this constriction is likewise at 'most equal to the amount of reduction in the thickness of'wall.

-We claim:

1. In a tube rolling' apparatus, a plurality of rolls shaped for the production of a relatively thin walled tube from a hollow metal body having a relatively thick wall, a cylindrical mandrel, each-roll being shaped to provide a roll pass gap between the mandrel and the rolls, each roll having an introducing and reducing cone-shaped portion joined in a step-like' manner with a substantially cylindrical-shaped portion for elongating the hollow metal body and each roll having a smoothing part, and the maximum height and length of the step-like portion being equal to the reduction in wall thickness to which the hollow n :0-

body is to be subjected.

2. In tube rolling apparatus according to claim 1 wherein the introducing and reducing coneshaped portion is arranged at an angle of less than 30 degrees with respect to the mandrel, and

each roll having a further conical portion adjacent the roll pass gap which slopes at an angle not exceeding 10 degrees with respect to the mandrel.

FRITZ KOCKS.` JOSEF MERREN. 

